Mutual coupling



Nov. 6, 1945. 'R, F, SHEA 2,388,295

MUTUAL COUPLING Filed July 2, 1945 Invenfiof; I 1 Richard F: Shea,

Patented Nov. 6, 1945 Richard F. Shea, Fairfiel d, Conm,- assignorito General" Electric Gompany; a. corporation of i New York ApplicationJuly 2, 1943',-Serial No...493,317

(Cl."'I71 119) G'Claims.

I .My inventionrelates-toradio:receiving apparatus andsin:particularxto circuitccoupling arrangements for such apparatus.

It is well known in. radio receivers to use magnetic .body members: of compressed-powdered iron. particles as housings and cores .for: transformers of radio frequency currents. From armanufacturing; pointof view, it is desirable to provide in 'such. a transformer molded cores andpolepieces of astandard size .and shape so that thetransormerwindings may-be quickly. and easily placed 1n operating position and that adjustment of the self inductance. of individual windings-may '-be accomplished by means of a singletuning core for each winding, the mutual inductance .being established principally.- by the :geometric proportions of the housing, pole pieces. and cores. When unitary housings forrthe-windings ofzthertransformer sware-prdu(3ed in large; quantities,.it is 1mposs1ble to obtain the..uniformity.- of/sizes and materials necessary for the critical valueoimutual inductance required for radio frequency transformers. Accordingly, it is an object of. my

. invention to provide an improved mutual coupling arrangement for a radio-frequency transformer.

It is another object of my invention to provide an improved coupling arrangement'for a. radio frequency transformer in which adjustmentof the mutual inductance of the transformenwindings may be efiected easily-andaccurately during the initial-tuning of the receiver circuits.

- A further objectof my invention is-.to provide .an improved link coupling for the windings of a radio frequency transformer having aunitary powdered iron body member.

It is a still further object of .myinvention to provide an improved link coupling arrangement for a radio frequency transformer which likewise iunctions to shield adjacent receiver circuits from the high frequency fields surrounding the magnetic structure of the transformer.

One of the-features of my invention is the use, in conjunction withthe unitary. powdered iron structure of a radio frequency transformer, of a single turn winding encirclin the. magnetic structure and the windings ofthe transformer and adjustableto the position required to -.give a desired value of mutual inductancefor the transformer.

The features of my.invention which I believe to be novel are set forth withparticularity in the appended claims. My invention itself, however both as to its organization andmethodof operation, together with vfurther objects. andadvan---- stages :thereof; may -:best be understood by ref :erence. toz the-:followng description taken in:con

nectionvwith .zthe' accompanying drawing-tin -which Fig; lpis aside elevation view, partly in '-;section, of a transformer embodying my. invenction; Fig; 2 is a p1an:view ofiFig. 1-.along the line 2 2;. and Fig; 3-is aside-elevation VlBW'JOf a :modiflcation-of the transformer arrangement of Fig. 1.

.uReferring to Fig, l, I have shown a radio frenquency transformer comprisinga mainvbody rmember l0 having. a pair oferecesses H and-l2 itherein in which are located. aiprimary winding 13. and a secondary 'winding l4, the inductance .'.10f the individual windings *being adjusted -re- --spectively by means-of tuning cores l5. and J6.

.fI'he.;main body: member ID is preferably. a uni- .-tary structure formed jby'molding-or compressing and-machining powdered. iron particles, therecesses H and I2 appearing as substantially cy- ;.:'lindricalwholes:in this: unitary body member.

:? These: recesses are separated by a central wall- I 1 .of; the .body: member.

A longitudinal .cross secrtionofthebody member I!) thus is in the form :ofa T having, inaddition to thecentral wallll,

rend walls'lB and J9 and a base portion 20.

The-cylindrical recesses II and 42 have cen- ":trallydocatedopenings in their bottom walls surwounded ;-by a shoulder-portion 2| for receiving .ztubularcoilforms 22, :23,-;upon which are wound :the windings I3, I4. Thewupper or openends ':of thewrecesses II and I2 are likewise provided 'uwithshoulders 25 for receiving the circular clo- ;surezmembers or.pole pieces, 21.

'The. unitary-transformer structure thus. far

:zdescribed maybe supported from a radio chassis :-.30 by.-means of abolt 3| which passes through the-central wall l1: ofthe body member Ill. .The

Whose positions correspond to the Positions .of.the

minalboard of any suitable .insulating mate- .rial; preferab1y .-is clamped betweenv chassis 30 andthe'body member !0 by meansof bolt 3! and nut '36 .and hasriveted thereto a .pluralityoiterminal-posts 38 towhich are attachedthe leads *39 from. the transformer windings.

The termi- .al board 35llikew-ise functions to support the tun- .ing. cores 15 and! Sin an adjustable position with- .inthe tubular forms 22;23 by means of the tubularnuts'AO, 4i riveted to the terminal board and in threaded engagement with screws 42'; "43, aembedded. at .their lower ends, respectively, .in

...c0res l5','.l6. f'Ihe cores "l5, I6 are likewise provided with.s1ots.44,"45 .at their lower ends sothat the position of these tuning cores within the transformer windings may be adjusted in the usual manner by a screw driver.

In the transformer arrangement thus far described, the self-inductance of the individual windings l3, I4 is quickly and easily adjusted in the usual manner by means of the powdered iron tuning cores I5, I6. The mutual inductance of the windings in this unitary transformer structure is established principally by the geometric proportions of the walls l1, l8, IQ of the magnetic body member Ill, the thickness of the pole pieces 26, 21, and. the thickness of the bottom walls 20 and the cross sectional area of the tuning cores l5, I6. While this mutualinductance may be controlled to a larg extent by variation in design of the transformer, in actual production of transformers of this arrangement certain inevitable variations from desired values of mutual inductance are obtained, which variations are considerably greater than are permissible for the critical values of mutual inductance required for radio frequency transformers. In order to provide means quickly and easily to adjust the mutual inductance of the transformer windings precisely and accurately to a desired value, in accordance with my invention, a band or single turn 41 of conductive material, such as copper or aluminum, is placed around the external wall of body member Ill in a plane substantially parallel to a plane through the center line of windings l3, Id. The position of coil 41 on the external walls of the body member Ill is adjusted vertically until a desired value of mutual inductance is obtained. In general, a maximum value of mutual inductance is obtained when the coil 4! encircles the windings at their centers and this value is gradually reduced as the shortcircuited turn 41 is varied vertically up or down from this position.

The operation of the transformer described will be discussed with particular reference to its use as an intermediate frequency transformer in a radio receiver of the super-heterodyne type. The windings l3 and i4 each set up magnetic lines of flux A in the body member [0, which may be considered as flowing upwardly through the respective tuning cores l5, l6, radially outwardly through the respective pole pieces 26, 21, and vertically downwardly through the end walls l8, l9 and the center wall H. In addition to lines of flux flowing downwardly through the center wall [1, a certain proportion of lines from winding 13 flow across both closure members 26 and 21 and down through the tuning core l6. This additional flux constitutes flux lines B, which are mutual to the windings and give rise tomutual inductance between these coils. In a given transformer arrangement, as previously stated, the proportion of mutual flux to the total lines of flux is determined substantially by the dimensions of the magnetic paths between the windings.

The addition of the short-circuited winding or coupling link 41 is effective to disturb the flux arrangement thus far described. A considerable number of lines of magnetic flux A flows exteriorly of the walls l8, IS in the space outside the body member In to link the short-circuited turn 41 and induce a current therein. This current, in turn, sets up lines of flux C in a direction opposing the original lines A. These lines passing through coil l3 oppose lines A therein, slightly reducing its inductance. The lines C, which pass through coil I 4, however, are in the same direction as the lines B coming from coil l3 and therefore reinforce the lines B with the result that the mutual inductance of the coils is increased. In this manner the short-circuited turn 4! acts as a link coupling between the two coils. The value of the mutual inductance of the windings of the transformer is greatest when the coil 41 is in a central position on the external Walls of body member llland decreases in substantially the same amount with a given change in position either up or down from this central point. When a desired value of mutual inductance is obtained, the coil ll may be easily cemented, or otherwise secured, in a desired position on the outside of the transformer body H). In a given transformer structure, it has been found that, by varying the position of coil 41 from the bottom of the side walls l8, l9 to the center of these side walls, the mutual inductance may be increased per cent.

The plan view of the transformer arrangement of Fig. 1 shown in Fig. 2 illustrates the general configuration of the main body I0 and the relative sizes of the recesses ll, l2 and the walls l1, l8, Hi. It also shows the manner in which the short-circuiting turn ll is passed around the main body member ID adjacent the external walls of this body member.

In the modification of the coupling arrangement shown in Fig. 3, the transformer body member 10 is substantially entirely enclosed in a shielding can or housing 50 of conductive material, such as copper or aluminum. The shielding can 50 is provided with suitable apertures in its bottom surface to permit the adjustment of tuning cores [5 and [5 within the individual windings l3 and M. In order to provide means for adjusting the mutual inductance of the transformer, the shielding can 50 is provided with a vertical slot 5| which is substantially transverse to a plane through the windings within the transformer.

In adjusting the mutual inductance of the transformer arrangement shown in Fig. 3, the slot 51 is filled to a desired extent with any suitable conductive material 52, such as solder, until a desired value of mutual inductance is obtained. The housing 53 not only provides means for controlling the mutual inductance of the transformer windings without causing any substantial change in the self-inductance of the individual lines, but also functions substantially completely to shield adjacent receiver circuits from the high frequency fields surrounding the magnetic body member Ill 0f the transformer. In a given installation, when the body member l 0 is completely shielded by the housing or can 55, the self-inductance of the individual windings is changed by less than 10 per cent, while the mutual inductance of the windings may be varied over a range of 2 to 1. The selfinductances of the windings, of course, may be readjusted to desired values by means of the tuning cores I5 and I6.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since various modifications may be made, and I contemplate by the appended claims to cover any such -modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a radio frequency transformer comprising a body member of magnetic material having a plurality of recesses therein, said recesses being separated by a wall of said body member, each of said recesses having a corresponding winding of said transformer positioned therein, and magnetic closure members for said recesses, and a continuous loop of conductive material supported in fixed position adjacent the external walls of said body member and encircling said windings to provide desired mutual coupling thereof.

2. In combination, a radio frequency transformer comprising a body member of magnetic material having a plurality of recesses therein, said recesses being separated by a Wall of said body member, each of said recesses having a corresponding winding of said transformer positioned therein, and means for adjusting the mutual inductance of said windings, said means comprising a single loop of conductive material supported adjacent the external surface of said body member in a position encircling said windings.

3. In combination, a radio frequency transformer comprising a body member of magnetic material having a, pair of recesses therein, said recesses being separated by a wall of said body, each of said recesses having a winding of said transformer positioned therein, and means for adjusting the mutual coupling of said windings and for shielding said body member, said means comprising a casing of conductive material substantially enclosing said body member, said casing having in one wall thereof a slot substantially transverse to a plane through said windings, said slot being of a length suflicient to give a desired coupling of said windings.

4. In combination, a radio frequency transformer comprising a body member of magnetic material, a pair of windings positioned within said body member, and means for adjusting the mutual inductance of said windings comprising a loop of conductive material supported adjacent the external surface of said body member in a position encircling said windings.

5. A radio frequency transformer comprising a unitary magnetic body member, a pair of windings positioned within said member and separated by a wall thereof, and means for adjusting the mutual inductance of said windings comprising a continuous loop of conductive material supported adjacent the external surface of said body member in a position encircling said windings.

6. A radio frequency transformer comprising a unitary magnetic body member, a pair of substantially coplanar windings positioned within said member and separated by a wall thereof, a continuous loop of conductive material encircling said body member and substantially parallel with said windings, said loop being secured to the external surface of said body member in a predetermined position to obtain a desired value of mutual inductance of said windings.

RICHARD F. SHEA. 

